MultiAccessUnit reflector helper allocated once per ComponentStore

Bug: 365014948
Flag: EXEMPT bugfix

Test: atest android.mediav2.cts.CodecDecoderMultiAccessUnitTest
Test: atest android.mediav2.cts.CodecEncoderMultiAccessUnitTest
Test: atest android.mediav2.cts.CodecDecoderBlockModelMultiAccessUnitTest
Test: atest android.media.drmframework.cts.CodecDecoderMultiAccessUnitDrmTest
Change-Id: Icdf64821f81f09726467500667978dce6aa32857